Humid hydrophobic ionic liquids—widely used as electrolytes—have narrowed electrochemical windows due to the involvement of water, absorbed on the electrode surface, in electrolysis. In this work, we performed molecular dynamics simulations to explore effects of adding Li salt in humid ionic liquids on the water adsorbed on the electrode surface. Results reveal that most of the water molecules are pushed away from both cathode and anode, by adding salt. The water remaining on the electrode is almost bound with Li+, having significantly lowered activity. The Li+-bonding and re-arrangement of the surface-adsorbed water both facilitate the inhibition of water electrolysis, and thus prevent the reduction of electrochemical windows of humid hydrophobic ionic liquids. This finding is testified by cyclic voltammetry measurements where salt-in-humid ionic liquids exhibit enlarged electrochemical windows. Our work provides the underlying mechanism and a simple but practical approach for protection of humid ionic liquids from electrochemical performance degradation.

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Electrolyte composition can have significant influences on metal deposition. In this work we employ in‐situ scanning tunneling microscope (STM), together with electrochemical methods to investigate Cu deposition on Au (111) in ethaline containing CuCl2. Cyclic voltammograms in the Cu overpotential deposition regime are dominated by a rapidly rising cathodic current, accompanied by a preceding shoulder. Instantaneous nucleation and three‐dimensional growth are discerned for the Cu deposition at larger overpotential. In‐situ STM reveals the shoulder process is associated with the formation of monoatomic‐height clusters. Meanwhile, morphology evolutions of Cu nuclei along with time and potential are followed, and layered hexagonal and hexagon fortress shaped Cu nuclei and their growth are directly observed. Furthermore, atomic‐resolution imaging elucidates an ordered incommensurate (6×√79) adsorption structure on the surface of a Cu nucleus. Our observations are helpful in gaining deeper insights into the effect of deep eutectic solvents (DES) on Cu deposition at microscopic level.

Choline chloride (ChCl)-based-deep eutectic solvents (DESs) are widely used in electrochemical fields. In this work, the effect of two types of hydrogen bond donor (HBD) molecules, ethylene glycerol and lactic acid (LA), on electrochemical interfaces between the Au electrode and DESs has been investigated by employing voltammetry and electrochemical impedance spectroscopy. The anodic dissolution and passivation behaviors of the Au electrode are revealed in both ethaline and ChCl:LA. In ChCl:LA, the anodic dissolution of Au is slowed down, and the passivation film is relatively dense and stable due to the existence of the carboxyl group in HBD molecule LA. In the double layer region, the lifting and formation of Au(111) surface reconstruction and a disorder–order phase transition of the chloride ion adlayer were observed in the two DESs. Moreover, compared with ethaline, an extra pair of current peaks appears in ChCl–LA possibly due to the adsorption and desorption of LA on the Au(111) surface, which might imply the stronger interaction of LA with the Au electrode in ChCl:LA. HBD LA could even have marked an impact on the disorder–order phase transition of the chloride ion adlayer. The above results provide new insight into the significant effect of HBD molecules on the anodic dissolution and the passivation of the Au electrode and the electrochemical behaviors in the double layer region.

Ionic Liquids (ILs) and deep eutectic solvents (DESs) are promising candidate electrolytes in electrochemical fields due to their excellent properties. They can absorb water from the environment quickly, the existence of water in ILs/DESs benefits or harms their performance depending on the purpose of the applications. Therefore, studies on the effect of water on the properties of ILs/DESs have received much attention in recent years. This mini‐review provides an overview of the structure of the electrochemical interface in ILs/DESs incorporated with water by summarizing the information acquired from a variety of characterization technologies and simulations. Both our understanding of the interfacial structure and our perspective on further research in the field are presented.